Illuminating apparatus for operating microscopes generally use an illumination beam path (or illumination beam) which is at an angle in the region of about 6° to the observation beam path (or observation beam) (so-called 6° illumination). This avoids unwanted shadow formation which would occur in the presence of larger angles between the observation beam path and the illumination beam path.
Eye surgery places even more special demands on the illumination of a microscope. First of all, the image has sufficient plasticity at an illumination angle of about 6°. However, for certain ophthalmic observations or interventions it is necessary to produce the so-called red reflex. In this, the light reflected back by the retina causes the pupil of the eye being operated on to shine with a reddish light. This method of illumination is of major importance in cataract operations, for example, as any residual tissue can be identified particularly easily in the back light of the red reflex. The production of the red reflex requires smaller angles between the observation beam path and the illumination beam path, the preferred angles being in the range from 0° to 2° (so-called 0° or 2° illumination).
Operating microscopes which are constructed with two pairs of stereoscopic observation beam paths for a first observer (main surgeon) and a second observer (assisting surgeon) often have a deficiency in that the red reflex shows up very well for the main surgeon but only to an inadequate degree for the co-observer. The latter receives a good red reflex in only one of his two observation channels, either to the right or to the left of the main surgeon, depending on his position. This interferes with the stereoscopic observation.
DE 04028605 discloses an illuminating apparatus for a surgical microscope with an illuminating system which is arranged outside the optical axis of the microscope objective lens, and the operating field is illuminated through the microscope objective lens parallel to the axis of the objective lens, and a deflecting element on the side of the microscope objective lens remote from the object, which illuminates the operating field with a fraction of the illuminating light along the axis of the objective lens. This illuminating apparatus is characterised in that the illuminating system is equipped on the objective lens side with a reflecting element which reflects the illuminating light towards the microscope objective lens parallel to the axis of the objective lens, and the deflecting element illuminates the operating field at an angle of inclination to the axis of the objective lens which is less than the angle of inclination at which the reflecting element illuminates the operating field. The larger angle of inclination is preferably 6° here, while the smaller angle may vary from 0° to 6°. The illuminating apparatus described in this publication does not contain any solution, for example, to the problem of supplying a red reflex for a second observer (assisting surgeon).
DE 103 11 000 B4 discloses an illuminating apparatus for a microscope, particularly an operating microscope, having at least one observation beam path, with an illuminating system and a deflecting device for deflecting light emanating from a light source onto an object that is to be observed, e.g. an eye that is to be operated on, wherein the deflecting device allows the object to be illuminated at different illuminating angles with respect to the at least one observation beam, and wherein the deflecting device comprises two deflecting elements that are at least partially constructed as physical beam splitters. In order to provide a 6° and 2° illumination for a main surgeon and an assisting surgeon, this illuminating apparatus uses three deflecting elements.